One of the most difficult problems confronting Orthopaedic Surgeons is the reconstruction of large bone defects following trauma or tumor resection. In most cases, there is little doubt that the idea graft is a live piece of autogenous bone which reliably remains organized and alive and which defies resorption and maintains its original size and structural strength. Microvascular free living bone grafts satisfy these objectives and have been used clinically since 1975. However, despite the clinical application of the procedures, basic questions remain unanswered. The proposed study, employing microangiography, electronmicroscopy, fluorochrome bone labeling, bone scans, hydrogen washout techniques, should delineate the factors that influence the survival of the free, living bone graft and define its clinical place in reconstructive surgery.